A parallel computing strategy for the simulation of particulate flows with immersed boundary technique is proposed. This strategy can deal with the coupling between fluid and particle easily when particle crosses the boundaries of sub-domains which are decomposed from original computational domain. And a two- dimen- sional circular particle settling in a closed rectangular domain is simulated with the parallel technique and immersed boundary method to validate the parallel effi- ciency.
Without using any turbulent model, direct numerical simulation of a three-dimensional gas-solid two-phase turbulent jet was performed by finite volume method. The effects on dispersion of particles with different Stokes numbers by the transitional behavior of turbulent structures were investigated. To produce high-resolution results and reduce the computation and storage, the fractional-step projection algorithm was used to solve the governing equations of gas phase fluid. The low-storage, three-order Runge-Kutta scheme was used for time integration. The governing equations of particles were solved in the Lagrangian framework. These numerical schemes were validated by the good agreement be-tween the statistical results of flow field and the related experimental data. In the study of particle dis-persion, it was found that the effects on particle dispersion by the spanwise vortex structures were prominent. The new behaviors of particle dispersion were also observed during the evolution of the flow field, i.e. the transitional phenomenon of particle dispersion occurs for the particles with small and intermediate Stokes numbers.
Direct numerical simulation of coherent structures in the three-dimensional transitional jet with a moderate Reynolds number of 5000 was conducted. The finite volume method was used to discretize the governing equations in space; the low-storage, three-order Runge-Kutta scheme was used for time integration. The comparisons between the statistical results of the flow field; the related experimental data were performed to validate the reliability of the present numerical schemes. The emphasis was placed on the study of the spatial evolution of the three-dimensional coherent vortex structures as well as their interactions. It is found that the evolution of the spanwise vortex structures in three-dimensional space is similar to that in two-dimensional jet. The spanwise vortex structures are subject to three-dimensional instability; induce the formation of the streamwise; lateral vortex structures. Going with the breakup; mixing of the spanwise vortex structures, the streamwise; transverse vortex tubes also fall to pieces; the mixing arranged small-scale structures are formed in the flow field. Finally, the arrangement relationship among the spanwise, the streamwise; the lateral vortex structures was analyzed; their interactions were also discussed.
